Denver's $12 million offering of "mini-bonds" sold out in about an hour Monday at the start of what was supposed to be a five-day sale.

"It was really quick," said Wil Alston, spokesman for the Denver Department of Finance.

Purchases of the $500 bonds appeared to be limited to online buyers who acted fast and others who hand-delivered order forms ahead of the 8 a.m. sale, Alston said.

That left everyone else out of luck. Some callers to The Denver Post expressed frustration that the bonds went on sale online two hours before they were to be available at a city-designed Vectra Bank branch.

Only Colorado residents could buy the bonds, and the city set a limit of 40 bonds per person, or $20,000 worth. Alston said preliminary estimates put the number of buyers around 1,000, meaning the average buyer bought roughly 24 bonds. Firmer figures will be available when sales are processed in the next week or two.

The mini-bonds, offered for the fifth time since 1990, were divided into two categories, both costing $500 and offering tax-free interest. A nine-year bond earns a 50 percent return in nine years, paying back $750 upon maturation. And a 14-year bond doubles, paying back $1,000.

The mini-bonds will finance the final portion of the $550 million Better Denver Bond Program, approved by voters in 2007 to fix roads and civic buildings.

"We are pleased with the strong response from Colorado citizens," Deputy Mayor Cary Kennedy, also the city's chief financial officer, said in a news release issued Monday afternoon. "Coloradans have proved once again they value the investments we are making in Denver and want to be a part of Denver's success."

A message on the city's website after the bonds were sold out said: "Thank you, Colorado, for your overwhelming response to the 2014 Denver Mini-Bonds. Coloradans purchased all of the Denver Mini-Bonds available — a total of $12 million — before the end of our planned order period.

"We are thrilled to be able to use the proceeds from these bonds to complete the final phases of the Better Denver projects approved by Denver voters, particularly improvements to the city's outstanding cultural facilities."

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